Diesel Performance Basics

Diesel Performance for Beginners

The basics of diesel performance focus on reducing pumping losses in the intake and exhaust systems. If you treat an internal combustion engine as a giant air pump, the less restriction into and out of the pump, the more efficiently it will operate. On a diesel engine, reducing restriction in the intake and exhaust system will free up usable power, increase turbocharger response/performance, and pave the way for future power adding mods.

Diesel Performance Air Intake

An aftermarket cold air intake is likely one of the easiest components to install on your Cummins, Duramax, or Power Stroke diesel. These kits are completely bolt on and require no additional modifications. The term "cold" air intake can be misleading, as these don't necessarily draw air that is any cooler than what the factory airbox provides. The primary benefit is reduced restriction, which translates into improved turbocharger response (reduced turbo lag), marginally better airflow, and reduced exhaust gas temperatures (EGT).

There are a vast number of air intake options available; you'll need to decide between an oiled or dry filter and an open or enclosed airbox. Intake systems with some form of heat shielding are highly recommended. Having used dry and oiled filters, we've been satisfied with the results from both. Our recommendation is to focus on filtration, as turbocharger compressor wheels do not respond well to dust. The performance difference between a performance focused and filtration focused filter are marginal at best.

Intake Elbow/Air Horn

An intake elbow or air horn is essentially the adapter between the intercooler/turbocharger tubing and the intake manifold. The component will vary in size and shape by application, but it's typically a restrictive fitting. The aftermarket has responded with a variety of less restrictive parts and, in some instances, has improved the thermal properties in order to reduce heat flow into the incoming air charge. Aftermarket units typically feature smoother transitions and optimized geometry to allow air to flow with less turbulence and pumping losses. Most are also optional with pre-tapped ports for injectables like water methanol. If you're installing an aftermarket intake system, you may as well finish it off with a high flow air horn.

Performance Diesel Exhaust System

With the exception of DPF equipped trucks, there are two types of diesel exhaust kits:

Turbo-back exhaust system: Turbo-back exhaust kits replace the entire factory exhaust system from the turbocharger to the tailpipe, including the downpipe (coming off the turbocharger). This is an option for trucks with exhaust systems that do not have any emissions devices. For trucks with emissions devices, these may be an offered but will delete any factory emissions aftertreatment systems and are designed for offroad/race use only.

Cat-back exhaust system: Cat-back exhaust kits replace the factory exhaust system from the outlet of the DOC (diesel oxidation catalyst) to the tailpipe, retaining the factory downpipe and plumbing from the turbocharger outlet to the DOC. Since the factory downpipe is often restrictive, these kits do less for performance than turbo-back systems. However, they remain emissions compliant. To get the most from a cat-back system you'll want to replace the factory downpipe, even if you plan on retaining the DOC.

Diesel Lift Pump

If additional modifications are in your future, now is a great time to address the factory lift pump. A lift pump is the low pressure fuel pump in a diesel fuel system; its job is to move fuel from the fuel tank to the injection pump. Higher fuel flow demanded by larger injectors, tuning, or modified injection pumps can tax the factory lift pump. If the lift pump fails to meet this demand, it could reduce performance and even worse, cause injection pump failure from starvation.

An aftermarket lift pump will outflow the factory pump and meet the delivery demand of your fuel system modifications. However, there are many "fuel systems" on the market that accomplish much more. These units have their own integrated filtration system. Not only do they filter debris and particulates from diesel fuel, they separate air and water from the fuel. The end result is higher fuel quality, fuel system protection, and more fuel flow than you will ever need. If you want to get the most from your setup a lift pump, filtration system combination is the way to go.